Among image processing technologies, a technology of reducing random noise contained in an image is indispensable for reproducing the captured image more clearly. One technology of reducing such random noise is disclosed in, for example, PTL 1.
The technology described in PTL 1 is configured by using: a plurality of arithmetic circuits calculating the number of pixels ‘n’ for moving average based on a preset mathematical equation with respect to an arbitrary attention pixel ‘i’ in a main scanning direction in a color digital signal outputted from an input image processing circuit; a plurality of bit selection circuits selectively outputting the attention pixel ‘i’ and ‘n’ reference pixels ‘j’ preceding and following the attention pixel ‘i’; a plurality of differential circuits calculating absolute values of differences between an output level of the attention pixel ‘i’ and respective output levels of the reference pixels ‘j’; a plurality of judgment circuits outputting the attention pixel ‘i’ as well as comparing values outputted from the plurality of differential circuits with a preset threshold value stored in a threshold storage memory to output reference pixels ‘j’ based on the comparison result; and a plurality of arithmetic circuits performing moving average processing on output signals outputted from the plurality of judgment circuits.
In other words, with a configuration to add a reference pixel ‘j’ to the moving average processing only when the absolute value of a difference between output levels of the attention pixel ‘i’ and a reference pixel ‘j’ is equal to or less than the threshold value, any portion where the absolute value of the difference exceeds the threshold value representing an abrupt change is excluded from the moving average processing, and thus a noise component can be removed effectively.